1. Field of the Invention
The present invention relates to an adjustable shock absorber, particularly for use with motor vehicles, which includes a cylinder containing damping fluid, a piston rod which projects into the cylinder in a sealed manner and moves axially, and a piston attached to the piston rod and dividing the cylinder into two working chambers, the shock absorber being provided with at least one passage producing a damping force, the effective cross section of which can be adjusted by a throttle valve.
2. Description of the Prior Art
German Laid Open Patent Application DE-OS No. 21 19 531 relates to a hydraulic adjustable shock absorber well known in the prior art in which there is a first damping element, plus a line equipped with a control valve. There is also a control valve and a damping element in a closed circuit, always separately located. The control valve is set manually or by the action of one of the vehicle mechanisms. One disadvantage of devices of this type is that they are difficult to manufacture from a production engineering point of view, due to the line and due to the components being arranged in series. Additionally, the mechanical activation produces a certain damping force, such that reliable variability in the different damping characteristics cannot be achieved.
German Patent Publication Published for Opposition Purposes DE-AS No. 12 42 945 relates to another hydraulic shock absorber well known in the prior art, the damping characteristics of which can be adjusted by changing the flow of the hydraulic damping medium electromagnetically by means of a damping valve. In this device, there are two bypass connections, the first of which is generally used to regulate the damping force in the decompression stage, as opposed to the compression stage. A disadvantage of this configuration is that there is no provision for regulating the compression stage, and such a regulation is not possible in this design.
German Laid Open Patent Application DE-OS No. 33 34 704 relates to known prior art shock absorbers having a control apparatus to regulate the damping valves in the damping piston. By means of an electromagnetic drive, a return force is produced on the throttle valve. Additionally, there is a supporting hydraulic compensation apparatus reinforcing this return force. A disadvantage of this configuration is that the force produced by the fluid pressure is not applied directly to the throttle element, but via a supporting body, necessitating a seal, which produces friction and which, therefore, interferes with the opening and closing action of the valve, or else produces a significant oil leakage flow.
All of the aforementioned patents are incorporated by reference as if the entire contents thereof were fully set forth herein.